Sometimes an arc generated on turning on a contact of the electromagnetic relay switch causes deposition of the contact to generate a trouble that the contact remains in an on state even if a power supply is turned off. There is well known a configuration in which, in order to detect the deposition of the contact of the electromagnetic relay switch, current is passed through the excitation coil to turn on and off the contact, and the deposition of the contact is detected by actually checking the on and off states of the contact.
However, there is a strong demand to detect existence or non-existence of the deposition while the contact is not turned on, namely, the contact of the electromagnetic relay switch is kept in the off state.
A conventional configuration in which the existence or non-existence of the deposition is detected while the contact of the electromagnetic relay switch is kept in the off state will be described below. FIG. 10 is a circuit diagram illustrating a conventional deposition detection device. The deposition detection device includes a battery 91 in which plural battery units 92 are connected in series, a contactor 93 that is connected in series to positive-side and negative-side outputs of the battery 91 to supply power to a load 40, a control circuit 94 that controls the on and off states of the contactor 93, and a deposition detection circuit 95 that detects the deposition of the contact 80 of the contactor 93.
The contactor 93 includes a positive-electrode-side contactor 93A that is connected onto a positive side of the battery 91 and a contactor 93B that is connected to an output on a negative electrode side. The load 40 is a motor 43 and a power generator 44, which are connected through a DC/AC inverter 42, and the load 40 has a large-capacity capacitor 41 on a primary side of the DC/AC inverter 42.
The positive-electrode-side contactor 93A is connected between the positive electrode side of the battery 91 and a positive-electrode output terminal 99, and the negative-electrode-side contactor 93B is connected between the negative electrode side of the battery 91 and a negative-electrode output terminal 99. Each of the positive-electrode-side contactor 93A and the negative-electrode-side contactor 93B includes an excitation coil 81 that controls the on and off states of the contact 80. The positive-electrode-side contactor 93A and the negative-electrode-side contactor 93B are relays each of which includes the excitation coil 81 so as to be able to be independently controlled. In the positive-electrode-side contactor 93A and the negative-electrode-side contactor 93B, the contact 80 can be turned on while the excitation coil 81 is energized, and the energization of the coil 81 is stopped to turn off the contact 80.
When an ignition switch is turned on, the negative-electrode-side contactor 93B is switched to the on state while the positive-electrode-side contactor 93A is kept in the off state. At this point, the power supply precharges the capacitor 41 using a precharge circuit 96 connected in parallel to the positive-electrode-side contactor 93A. After the capacitor 41 is precharged, the positive-electrode-side contactor 93A is switched from the off state to the on state, and the running battery 91 is connected to the load 40. Then a precharge contactor 98 of the precharge circuit 96 is switched to the off state.
The precharge circuit 96 is a series-connected circuit including a precharge resistor 97 and the precharge contactor 98, and the precharge circuit 96 is connected in parallel to the positive-electrode-side contactor 93A. The precharge contactor 98 is switched to the on state before the positive-electrode-side contactor 93A is switched to the on state, and the capacitor 41 is charged using the running battery 91. The precharge resistor 97 restricts the current with which the running battery 91 charges the capacitor 41. The precharge circuit 96 charges the capacitor 41 while restricting the charge current using the precharge resistor 97.
The ignition switch of a vehicle is turned off, the control circuit 94 switches the contactor 93 to the off state. The control circuit 94 intercepts the energization of the excitation coils 81 of the positive-electrode-side contactor 93A and negative-electrode-side contactor 93B, namely the control circuit 94 puts the excitation coil 81 into a non-energized state, and the excitation coil 81 is switched to the off state. When the excitation coil 81 is in the non-energized state, the contactor 93 is switched to the off state in the normally operating state. However, in the contactor 93 in which the contact 80 is deposited, the contact 80 is not switched to the off state but kept in the on state while the excitation coil 81 is not energized.
In the state in which the control circuit 94 puts the excitation coil 81 into the non-energized state, a deposition detection circuit 95 detects whether the contactor 93 is switched to the off state, namely, whether the contact 80 of the contactor 93 is deposited. The deposition detection circuit 95 detects the inductance of the excitation coil 81, and detects the deposition of the contactor 93 using a value of the inductance.
FIG. 11A is a sectional view illustrating the on state (deposition state) of the contactor 93 in which the existence or non-existence of the deposition is detected, and FIG. 11B is a sectional view illustrating the off state of the contactor 93.
As illustrated in FIGS. 11A and 11B, the contact 80 of the contactor 93 is reciprocated by the excitation coil 81. Accordingly, a position of the contact 80 identifies a position of a plunger 82. At this point, FIG. 11A illustrates the on state of the contact 80 of the contactor 93, and the on state of the contact 80 is identical to the state in which the contact 80 is deposited. FIG. 11B illustrates the off state of the contact 80 of the contactor 93. The position of the plunger 82 changes the inductance of the excitation coil 81. This is because the plunger 82 is inserted in the excitation coil 81 to change the position of the plunger 82. In the contactor 93 in which the excitation coil 81 attracts the plunger 82, the plunger 82 attracted by the excitation coil 81 decreases a magnetic resistance of the excitation coil 81 to increase the inductance. In the contactor 93 of FIG. 11A, the inductance of the excitation coil 81 is increased in the energized state of the excitation coil 81. This is because the plunger 82 is deeply inserted in the excitation coil 81. As illustrated in FIG. 11B, the inductance of the excitation coil 81 is decreased in the non-energized state of the excitation coil 81. This is because the plunger 82 is ejected from the excitation coil 81 by a spring 83.
Accordingly, the deposition detection circuit 95 detects the inductance of the excitation coil 81 to be able to detect the position of the plunger 82, namely, the position of the contact 80. The plunger 82 is located at the position where the contact 80 is turned on when the excitation coil 81 has the large inductance, and the plunger 82 is located at the position where the contact 80 is turned off when the excitation coil 81 has the small inductance.
Therefore, the deposition detection circuit 95 detects the inductance of the excitation coil 81 to be able to detect the position of the plunger 82, namely, the on position and the off position of the contact 80 from the value of the inductance. In the non-energized state of the excitation coil 81, a determination of the deposition in which the contact 80 is located at the on position is made when the excitation coil 81 has the large inductance. This is because the excitation coil 81 has the small inductance in the non-energized state of the excitation coil 81.
FIG. 12 illustrates a configuration of the deposition detection circuit 95 of the power supply in FIG. 10, and FIG. 13 illustrates an operating principle that the deposition detection circuit 95 in FIG. 12 detects the inductance. The deposition detection circuit 95 includes a capacitor 84 that is connected in series to the excitation coil 81 of the contactor 93, and an AC power supply 85 that supplies detection voltage of the inductance to the series circuit including the capacitor 84 and the excitation coil 81. While the AC power supply 85 supplies AC power to the series circuit including the capacitor 84 and the excitation coil 81, the deposition detection circuit 95 detects the voltage induced at both ends of the excitation coil 81 to detect the inductance.
The voltage induced in the excitation coil 81 is increased in proportion to the inductance. Accordingly, the induction voltage of the excitation coil 81 is detected by the differential amplifier 86, and the induction voltage is input to a discrimination circuit 87 to be able to detect the inductance. As described above, the inductance of the excitation coil 81 in which the contact 80 is turned on is larger than the inductance of the excitation coil 81 in which the contact 80 is turned off. The induction voltage of the excitation coil 81, which is detected by the differential amplifier 86, is higher in the on state of contact 80 than that in the off state of the contact 80. Therefore, the discrimination circuit 87 compares the induction voltage input from the differential amplifier 86 to a setting voltage, the determination that the contact 80 is in the on state is made when the induction voltage is higher than the setting voltage, and the determination that the contact 80 is in the off state is made when the induction voltage is lower than the setting voltage.